1. Field of the Invention
The present invention provides a multi-band antenna of compact size, in particular a monopole antenna of a compact size with a three-dimensional bending structure that uses a characteristic of coupling effectively between different frequency bands to improve the antenna's efficiency.
2. Description of the Prior Art
In a modern world of information, various wireless communication networks have become one of the most important channels for exchanging sounds, text, numerical results, data, and video for many people. An antenna is required to receive information carried by wireless electromagnetic waves in a wireless communications network. Therefore the development of antennas has also become one of key issues for vendors in the technology field. In order to have users implement and access information from different wireless networks in ease, an antenna with better design should be able to cover different bands of each wireless communications network with only one antenna. Besides, the size of the antenna should be as small as possible to be implemented in compact portable wireless devices (such as cellphones, Personal Digital Assistants i.e. PDAs).
In the prior art, Planar Inverted-F Antennas (PIFAs) are the most popular for wireless communication network transceiving services. Please refer to FIG. 1. FIG. 1 is a diagram of an antenna 10 that is a typical PIFA. A PIFA generally uses a planar radiation portion and a planar base to induce an electromagnetic wave oscillation. In addition, an antenna as shown in the R.O.C. patent publications number 20041 9843 (corresponding to U.S. Pat. No. 6,930,640) is also a type of PIFA. However, when using this type of antenna as a multi-band antenna, a planar radiation portion of the antenna requires a large planar area, and a distance between the radiation plane and a base plane of the antenna d0 (as in FIG. 1 ) is related to a frequency/bandwidth of the antenna that cannot be adjusted as desired. Thus, the antenna of the prior art cannot be structurally reduced in size and is unable to meet the needs of compactness and multi-band reception.